The present invention relates generally to handheld power tools, and specifically to fastener driving tools, including, but not limited to combustion-powered fastener-driving tools, also referred to as combustion tools or combustion nailers, as well as pneumatic nailers and electric nailers employing reciprocating driver blades and magazine feeders.
Combustion-powered tools are known in the art, and one type of such tools, also known as IMPULSE® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439; 6,145,724 and 7,341,171, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslodeu of Vernon Hills, Ill. under the IMPULSE®, BUILDEX® and PASLODE® brands.
Such tools incorporate a tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a single cylinder body. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
When the user depresses the tool against a workpiece, the tool closes the combustion chamber and fuel is delivered into the combustion chamber, after fuel/air mixing, the user activates the trigger, initiating a spark with the ignition spark unit, then the burnt gas generates a high pressure to push the piston down and drive the nail. Just prior to the piston impacting the bumper, the piston passes through the exhaust port, and some of the gas is exhaust. The combustion chamber generates vacuum pressure to retract the piston back to the pre-firing position. Simultaneously, the fastener feeding mechanism feeds the next fastener into a pre-driving position in the nosepiece or nose (the terms are considered interchangeable). However, due to friction caused by the feeding mechanism urging fasteners against the driver blade, the return of the piston is slowed or even stopped.
More specifically, once the nail driving process is complete, a subsequent timing relationship between the return of the drive piston and advancement of the feeder mechanism is also important to obtain reliable piston return and nail feeding. The preferred timing scenario is for the drive piston to return to the pre-firing position before the feeder mechanism advances the nail into the tool nosepiece. In conventional nailers, the feeder mechanism attempts to advance the nail into the nose while the drive piston and driver blade is returning to the pre-firing position. This results in the nail being biased against the driver blade during the return cycle. Only when the driver blade is fully retracted to its pre-firing position and a clear fastener passageway is provided does the fastener reach its drive position.